A general display device comprises a display panel, a circuit board, a light source device and the like. A light source device that irradiates light from the rear surface thereof is either a side light type (edge light type) including a light source on the side surface of an enclosure or a direct type including a light source on the bottom of an enclosure in a position opposed to a display panel.
Some of the side light type light source devices use a light guide plate in order to guide light from a light source to an opening of an enclosure. A light source device using a light guide plate propagates, inside the light guide plate, light emitted from a linear light source such as a cold-cathode tube or a point light source such as a light emitting diode (hereinafter referred to as an LED) and diffuses the light by way of a diffusion pattern provided in the light guide plate to take out the light in the shape of a plane at the opening of the enclosure.
With a light source device using a point light source such as an LED as a light-emitting element described above, the luminance of a display screen is enhanced by increasing the number of point light sources thus increasing an element density or increasing the current supplied to each point light source. In any way, heat from each point light source caused by light emission brings the periphery of the point light source at high temperature.
There is proposed a light source device including a light source substrate mounting heat-dissipating means, the light source substrate composed of a flexible printed circuit board (hereinafter referred to as an FPC) mounting point light sources and a wiring pattern to feed power to each light source (for example, Patent Reference 1 (Japanese Published Unexamined Patent Application No. 2006-210183) and Patent Reference 2 (Japanese Published Unexamined Patent Application No. 2002-229022)). A surface lighting device 1 disclosed in Patent Reference 1 is arranged so that a heat-transmitting part 10a provided in a recessed part 10 formed on the side wall 8 of a frame 6 made of a metallic material will come into contact with a mounting surface 3d of each of the point light sources 3 thus receiving the light sources 3 in the recessed part 10. An FPC 4 as a light source substrate and the point light sources 3 are fixed together with a conductive adhesive 12. The technique disclosed in Patent Reference 1 uses this arrangement to efficiently transmit heat generated by the light emission of the point light source 3 by way of a metallic frame 6 thus enhancing the heat dissipation, which allows the element density of the point light source 3 and the current supplied to each point light source 3.
In a backlight device disclosed in Patent Reference 2, a soft metallic sheet 7 for dissipating heat from a light-emitting diode 2 formed in almost the same shape as a film wiring board 4 is bonded with adhesive to a surface opposite to the surface of the film wiring board 4 on which the light-emitting diode 2 is mounted, thus covering a metallic reflector 8. The technique disclosed in Patent Reference 2 uses this arrangement to effectively transmit heat generated on the light-emitting diode 2 as a light source to the film wiring board 4 and a heat-dissipating member such as the soft metallic sheet 7 without letting the heat fill the backlight device itself.
However, the light source devices disclosed in Patent Reference 1 and Patent Reference 2 have following disadvantages. For example, although a light source substrate and a heat-dissipating member are fixed together with an adhesive, the adhesive peels off over time.
When a metallic plate such as an MCPCB (Metal Core Printed-Circuit Board) is used for a light source substrate in order to prevent the peel-off, the resulting cost is higher than that of using an FPC.    [Patent Reference 1] JP-A-2006-210183 (Pages 2-5, FIGS. 1-4)    [Patent Reference 2] JP-A-2002-229022 (Pages 3-7, FIGS. 1-4)